Autoselect a port rather than always using 8080 for chrome_test.

test/runner/browser/chrome_test.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:unittest/unittest.dart';
 import 'package:unittest/src/runner/browser/chrome.dart';
 import 'package:unittest/src/util/io.dart';
@@ skipping 99 matching lines @@
               webSocket.first
                   .then((message) => expect(message, equals('null')))
                   .whenComplete(chrome.close),
               completes);
         }
       }, count: 2));
     });
   });
 
   test("a process can be killed synchronously after it's started", () {
-    return shelf_io.serve(expectAsync((_) {}, count: 0), 'localhost', 8080)
+    return shelf_io.serve(expectAsync((_) {}, count: 0), 'localhost', 0)
         .then((server) {
       var chrome = new Chrome(baseUrlForAddress(server.address, server.port));
       return chrome.close().whenComplete(server.close);
     });
   });
 
   test("reports an error in onExit", () {
     var chrome = new Chrome("http://dart-lang.org",
         executable: "_does_not_exist");
     expect(chrome.onExit, throwsA(new isInstanceOf<ProcessException>()));
   });
 }